Disposition of fly ash, which is essentially fine solid non-combustible mineral residues (not to be equated with bottom ash, cinders, or slag) from coal-burning installations such as power generating plants is an increasingly difficult problem. Recent and increasingly strict environmental restrictions pertaining to the handling and final placement of fly ash, and the currently available technology (which was developed without prime importance being attributed to environmental considerations) have combined to make the wasting of fly ash a source of rapidly escalating costs and environmental concerns common to nearly all coal-burning plants.
One of the greatest sources of fly ash, and a source which invariably impinges heavily on populated areas, is power generating facilities. Accordingly, the invention of this application will be described in terms of the handling (in a transporting sense) and the treatment of fly ash which is generated at a power station. It should be understood however that the inventive concepts described herein are applicable to any source of fly ash generation.
Two methods of wasting fly ash which have been utilized in connection with power plant operations are the "conditioning" method, and the "water solution" method.
In the conditioning method of wasting fly ash, just sufficient water is added to the bone dry (less than one percent moisture content) fly ash to calm the dust. Although the ratio of the weight of water added to the total weight of the fly ash and water product (which is hereafter referred to as the water content) will vary with the type of fly ash (which of course varies with the type or types of coal burned in the boiler, and its condition--i.e.: crushed or pulverized), a water content of about 20 percent is the maximum upper limit of water used in the conditioning process.
The water solution of wasting fly ash requires a water content of about ninety percent.
The conditioning system is becoming less and less suitable to today's needs since fugitive dust is always a problem no matter how carefully the process is monitored, and handling problems are invariably encountered. For example, if the fly ash is damped or conditioned at the power station prior to transportation to the final disposal site, it may be impossible to dump the conditioned fly ash from the haulage vehicle at the disposal site. Conditioning fly ash is also a very expensive system since much heavy equipment, such as bulldozers, must be employed, and after-placement problems, such as leaching, is ever present.
The water solution process requires large quantities of water. On many occasions such quantities are simply not readily available, or only available at very high costs, such as in arid climates. Further, expensive site preparation procedures, such as cell liners, must be employed.
Accordingly it is the primary object of this invention to provide a process and system for wasting fly ash which is economical, environmentally acceptable, and avoids at least the major disadvantages of all currently known systems, including the conditioning and water solution processes described above.
A specific object of the invention is to provide a method of and system for wasting fly ash whereby the fly ash is handled in transit to, and at the disposal site, in a manner which eliminates all fugitive dust.
A further object is to provide a method of wasting fly ash in which the final mixture will have a moisture content of about 25 percent to 50 percent, or the equivalent flowability thereof, and in which the moisture content and the bulk density of the mass will be uniform throughout.
Another object of the invention is to provide a process of wasting fly ash and a system therefor which results in no bleed water being generated at any point in the process.
Yet another object is to provide a fly ash wasting system which lends itself to chemical control of sulfate residues, which is particularly advantageous in connection with handling fly ash from high sulphur coal.
Yet a further object is to provide a process and system of wasting fly ash in which the processed fly ash can be pumped without clogging pipe lines for up to several thousand feet and yet, after placement, will harden into a stable mass which will support significant structural loads of up to several thousand pounds per square foot.
Yet another object is to provide a fly ash wasting system in which the final, hardened product meets all current environmental requirements, and is virtually impervious to percolation from gound water and rainfall whereby the pollution potential in the disposal area is virtually eliminated.
Yet a further object is to provide a fly ash wasting system in which on-site dust at the disposal location is reduced to a minimum because aggregate handling equipment, such as bulldozers, truck deliveries, compaction equipment and grading equipment (all of which are utilized in current wasting systems) are completely eliminated.
A further object is to provide a fly ash wasting system and process which is more economical to operate then many conventional systems due to the above advantages whereby special precautionary measures to protect against dust, etc. are eliminated, and capital equipment and labor costs are lower than in most, if not all, current wasting systems.